This disclosure relates generally to systems and processes useful for facilitating repair and maintenance of sea valves and other components on marine vessels, particularly large vessels, including vessels used for floating storage (FSO's) and production (FPSO's), while in the water. Specifically, the systems and processes described herein relate to facilitating repairs and maintenance of sea valves, and other components, on marine vessels by closing openings in the hulls of marine vessels to permit dry access to the sea valves and other components which are normally in direct communication with the openings.
Many large marine vessels, such as sea going ships, FSO's and FPSO's and the like, have openings in the hull below the waterline to allow inflow and outflow of water into cavities often referred to as sea chests. A sea chest is simply a cavity or chamber behind the hull of a marine vessel below the waterline that communicates externally with the water. The sea chest is often connected by plumbing such as piping and valves to convey water for various purposes within the ship. Such openings to the water are used for many purposes including drawing of water from the ocean for cooling and the like and for expelling water and other waste material into the ocean. The openings are typically connected by conduits and the like to pumps, valves, and other equipment within the engine room and other compartments of the vessel.
It is necessary to inspect piping and valves, and on occasion to replace or repair some of the plumbing or valves in and around the openings and leading to the openings. These repairs and reconstructions can be readily accomplished in dry dock. However, dry docks are frequently unavailable or are available only after a long wait. Moreover, putting a marine vessel in dry dock to perform such repairs and maintenance takes the vessel out of service, which usually results in substantial adverse financial affects.
Some sea chests require an affixed cover that may be opened and closed as needed while the vessel is in service. For example, many ships utilize maneuvering thrusters within sea chests from which water is ejected through hinged covers that act as a cover that opens to permit water to exit and closes to prevent water from entering the sea chest. Other sea chests do not have fixed covers and temporary covers are used to close the opening in the marine vessel hull to the sea chest when it becomes necessary to have dry access to the sea chest compartment while the vessel is in the water. Vessels with temporary covers require divers to properly place the covers over openings. This can be a hazardous operation, particularly in areas where there is restricted visibility.
U.S. Pat. No. 5,692,451 discloses sea chest covers fabricated from one or more viscoelastic materials such as polyethylene or polyurethane. The patent discloses that the visoelastic materials reduce corrosion and erosion as well as minimize marine organism growth and ice build-up on the covers. The covers disclosed in this patent are designed to be permanently affixed to a vessel.
U.S. Patent application 2004/0011265 A1 discloses sea chest covers made from viscoelastic materials that have been exposed to gamma radiation for enhanced strength. The application also discloses that the viscoelastic materials may also contain an anti-bacterial or anti algae growth additive. The covers disclosed in this patent are designed to be permanently affixed to a vessel.
U.S. Pat. No. 4,175,510 discloses a cofferdam for closing openings in hulls of vessels below the waterline. The cofferdam is a wooden structure that is lowered by a crane and guided in place by divers. The cofferdam may be secured to the hull of the vessel through attachment to a grating in the opening in the hull with a series of J-bolts.